This invention relates to an antenna unit mounted on a roof of a mobile body such as an automobile or the like and, in particular, to a protector-equipped antenna unit and an antenna protector for use in a digital radio receiver for receiving an electric wave from an artificial satellite (that may be called a “satellite wave”) or an electric wave on the ground (that may be called a “terrestrial wave”) to listen in a digital radio broadcasting.
In recent years, a digital radio receiver, which receives the satellite wave or the terrestrial wave to listen the digital radio broadcasting, has been developed and is put to practical use in the United States of America. The digital radio receiver is mounted on a mobile body such as an automobile and can receive an electric wave having a frequency of about 2.3 gigahertz (GHz) to listen in radio broadcasting. That is, the digital radio receiver is a radio receiver which can listen in a mobile broadcasting. Inasmuch as the received wave has the frequency of about 2.3 GHz, a reception wavelength (resonance frequency) λ thereof is equal to about 128.3 mm. In addition, the terrestrial wave is an electric wave in which a signal where the satellite wave is received in an earth station is frequency shifted a little.
The antenna unit must be attached to a roof of the mobile body in a case where the digital radio receiver is mounted in the mobile body such as the automobile.
In order to attach the antenna unit to the roof of the mobile body, an antenna unit with a protector is known in the art.
In a conventional protector-equipped antenna unit, the antenna unit is manufactured by making engineering changes with new specific antenna parts manufactured therefor. In other words, the protector-equipped antenna unit is manufactured by making engineering changes of a plurality of antenna parts constituting an antenna body so as to enable to mount a protector thereon and by assembling the plurality of antenna parts made engineering changes and a plurality of protector parts constituting the protector.
In addition, as an antenna unit without a protector, an antenna unit for use in a GPS (global positioning system) receiver for receiving a GPS signal is known in the art (see, e.g. JP 2001-68912 A) although the antenna unit is not for use in the digital radio receiver. It is noted that the antenna unit for use in the digital radio receiver and the antenna unit for use in the GPS receiver are similar in structure and in the outside shape each other because they have frequencies of received electric waves and radiation patterns (antenna patterns) which are slightly different from each other.
In the manner which is described above, the conventional protector-equipped antenna unit must be manufactured by making engineering changes of a specific antenna unit (antenna body). As a result, the conventional protector-equipped antenna unit is disadvantageous in that it takes cost and time.